1. Field of the Invention
This invention relates generally to a defocused unicell photometer with diffusion zone and, more particularly, to a defocused unicell photometer with diffusion zone for providing select directional response characteristics without increasing extreme field of view.
2. Background of the Prior Art
The use of unicell photometers for evaluating scene light to predict and/or control photographic exposures is well known. Such photometers generally consist of a photoresponsive transducer and a lens element for receiving actinic radiation from a scene and directing it onto a photosensitive surface of the transducer. The transducer may be either of the photovoltaic or photoresistive type and provides an output signal indicative of the actinic radiation incident to its photosensitive surface. The output signal from the transducer may thereafter be utilized to predict a photographic exposure condition or to actually control the closing of an automatic shutter blade mechanism at the appropriate film exposure condition. The output signal from such photometers is directionally responsive to the influence of actinic radiation from various scene objects within its field of view as based on their angular field position. Thus, brightly reflective scene objects which are located substantially on-axes with respect to the optical axis of the photometer contribute to a significantly greater portion of the output signal from the photometer than identical objects substantially displaced off the optical axis of the photometer. Since the directional response characteristic of most photometers is inherently so heavily weighted in favor of brightly reflective scene objects located substantially on-axis with respect to the optical axis of the photometer, it becomes generally desirable to suppress the on-axis response of the photometer while simultaneously increasing its off-axis response to provide a directional response substantially less sensitive to the position of a brightly reflective photographic subject in the field of view of the photometer.
One approach to suppressing the directional response of a photometer is utilized in Polaroid Corporation's SX-70 Land Camera which includes a photometer for controlling an automatic exposure control system as are more fully described in U.S. Pat. No. 3,810,201 entitled, "Automatic Return Mechanism for Manually Adjustable Trim Assembly" by E. H. Land et al., issued May 7, 1974 and U.S. Pat. No. 3,820,128 entitled "Flash Photographic Control System" by John Burgeralla et al., issued June 25, 1974. The photometer embodied in Polaroid's current SX-70 Land Camera comprises a forward lens element for directing incident actinic radiation to a photoresponsive transducer. In addition, there is also included a series of V shaped light diffusing grooves on one surface of the lens element which grooves operate to tailor the directional response curve for the photometer in a desired manner while simultaneously increasing the field of view of the photometer. However, while this increase in the field of view is perfectly acceptable for the SX-70 Land Camera, there may be instances where it is desirable to specifically tailor the directional response curve for the photometer without increasing the extreme field of view for the photometer.
Therefore, it is a primary object of this invention to provide an improved defocused unicell photometer wherein the directional response of the photometer is specifically biased in a particular direction within the photometer's field of view.
It is another object of this invention to provide and improved defocused unicell photometer wherein the directional response curve for the photometer is suppressed with respect to on-axis actinic radiation incident thereto while being simultaneously broadened with respect to incident off-axis actinic radiation incident thereto without any change in the extreme field of view of the photometer.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.